FEEDING-TISSUES 429 



containing a large amount of fat and protein. If these food-bodies are 

 carried off by ants, or artificially removed, the leaf-base develops a 

 fresh crop in the course of a few days. Morphologically considered, 

 the Miillerian bodies undoubtedly correspond to trichomes ; in 

 Schimper's opinion, it is probable that they represent modified glandular 

 hairs. Very similar structures (Beltian bodies), pear-shaped and of an 

 orange yellow colour, occur at the apices of the pinnules in Acacia 

 sphaerocephala (The Bull's Horn Thorn). These consist of a mass of 

 thin-walled parenchyma (storage-tissue) filled with protein and oil, and 

 are very readily detached from the leaf. 



The food-supply which plants offer to insects in return for their 

 valuable services as pollinating agents, generally takes the form of a 

 sugary secretion termed nectar : among the less specialised flowers, a 

 portion of the pollen may be sacrificed for the same purpose. Com- 

 paratively few flowers are provided with special feeding-hairs or 

 -tissues. 203 Arrangements of this latter kind are particularly preva- 

 lent in the Orchidaceae, and it is in connection with this family 

 that they have received most attention. In every case these attractive 

 devices occur in connection with the labellum, the perch upon which 

 insect-visitors alight ; and matters are always adjusted so that cross- 

 pollination must result, when the appropriate insect proceeds to devour 

 the feeding-tissue or -hair. 



This feeding-tissue was first discovered by Ch. Darwin in Catasetum; 

 his observations were subsequently confirmed by the author, while 

 more recently Porsch has made a detailed study of quite a number of 

 genera, such as Stanhopea, Maxillaria, C'irrhaea, Oncidium and Odonto- 

 glossum, with reference to these arrangements. The portions of the 

 labellum containing the feeding-tissue, develop into warts, knobs or 

 callosities of various shapes (Oncidium, Stanhopea), and may thus be 

 recognised even with the naked eye. These excrescences consist of 

 thin-walled cells which are filled with a variety of organic substances. 

 Non-nitrogenous reserve-materials are represented by starch (Catasetum), 

 amylodextrine (Stanhopea) or glucose, or sometimes by oil in globules 

 or larger masses. In addition, a large amount of protein-substance is 

 always present in the form of small granules, or more rarely in that 

 of crystalloids (Maxillaria lutescens, M. pumila) ; in the case of 

 Maxillaria varia, each cell contains a dense homogeneous mass of 

 protein-substance in the form of a layer adhering to its inner wall, as 

 well as numerous protein granules. Porsch mentions a very remark- 

 able adaptive feature of feeding-tissues, which consists in the fact that 

 the cuticle and the cutinised layers of the epidermal cells are oast off 

 at any early stage of development ; this arrangement naturally renders 

 the attractive food-material more readily accessible. 



